The goal of this research is to develop our fundamental knowledge of the basic mechanism(s) by which mononuclear phagocytes regulate proliferation of various normal cell types. Our findings to date suggest that macrophages and macrophage-like cell lines elaborate specific soluble factor(s) that can cause quiescent fibroblasts to initiate traverse of the cell cycle. Operationally, this monokine(s) is a "competence" factor, similar in its action to other known competence factors (platelet-derived growth factor and fibroblast growth factor) but biochemically distinct from both. We have concentrated our efforts on purification of the Macrophage-derived Competence Factor (MDCF) from spent supernates of cultured P388D1, a mouse macrophage-like cell line that elaborates generous amounts of MDCF in addition to another growth factor, interleukin-1 (IL-1). We have greatly simplified purification by adapting P388D1 cells to grow continuously serum-free in a defined medium. Serial application of ultrafiltration, gel filtration and ion exchange chromatography has clearly separated MDCF and IL-1 both in terms of biochemical/biophysical properties and biological activities. Analysis by silver-stained SDS-PAGE slab gels reveals two major bands of protein that correspond to MDCF activity and one that corresponds to IL-1 activity. Companion studies of affinity-purified IL-1 confirm our findings that MDCF and IL-1 are distinct biochemical and biological entities. Using this greatly purified MDCF, we are now beginning to develop specific antisera using rabbits and monoclonal antibodies using rat-mouse hybridomas to identify and quantify MDCF for in vivo and in vitro experiments. Our aim is to compare this monokine with other known growth factors as an initial step in using these as probes to dissect the cellular events associated with proliferation. The results obtained should provide a foundation for definitive studies on the relation of macrophage-derived competence factor production in vivo to lesions characterized by mononuclear phagocyte accumulation, extensive fibroplasia and collagen deposition.